Binding assay employing labelled reagent

Chemistry: molecular biology and microbiology – Measuring or testing process involving enzymes or... – Involving nucleic acid

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Details

435 5, 435 71, 536 243, C12Q 170, C12Q 168, G01N 3353, C07H 2104

Patent

active

055166350

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to binding assays employing a labelled reagent. Binding assays include immunoassays for the determination of concentrations of antigens in liquid samples, and it is also possible to use the present invention for the determination or detection of other analytes in liquid samples, including DNA sequences.
The present invention has particular relevance to non-competitive sandwich assays, that is to say assays in which a liquid sample containing an antigen or other analyte to be assayed such as a hormone is contacted with a first binding agent (such as an antibody) having binding sites on its molecule specific for the analyte whereby a fraction of the binding sites on the first binding agent representative of the concentration of the analyte in the liquid sample are occupied by the analyte. The fractional occupancy of the binding sites is then determined by a back-titration technique involving the use of a second binding material which is capable of binding with the bound analyte or with the binding sites occupied by bound analyte but not with unoccupied binding sites. Conveniently, the first binding agent will be referred to hereinafter as the capture binding agent and the second binding material will be referred to hereinafter as the developing binding material.
Non-competitive assays are to be distinguished from competitive assays in which the back-titration technique involves the use of a developing binding material which competes with the analyte for the binding sites on the capture binding agent, for example a labelled version of the analyte or another material able to bind with the unoccupied binding sites on the capture binding agent, although the present invention can also be used in such assays. In each case the extent of binding of the developing binding material is determined by the labelling of the developing binding material (or both that material and the capture binding agent), for example with a fluorescent label, and comparing the strength of the signal emitted by the bound labelled product of analyte bound to capture binding agent and developing binding material in the case of the unknown sample with the signal strengths achieved with corresponding samples of known analyte concentration which together provide a dose-response curve. One type of non-competitive sandwich assay involves the use of a labelled developing binding material and an immobilised capture binding agent which may or may not be labelled.


BACKGROUND ART

It is now well-recognised that non-competitive sandwich immunoassays generally display higher sensitivity than the more conventional competitive immunoassays. The widely accepted explanation for this higher sensitivity is the use of relatively large amounts both of the immobilised capture binding agent (usually an antibody located on a solid support) and of the labelled developing binding material (also often an antibody). By using large amounts of the antibodies, especially the capture antibody, the rate of reaction between analyte and capture antibody is increased, implying in accordance with the law of mass action that a greater amount of analyte is captured on the solid phase capture antibody in any specified time interval. Thus, the use of large amounts of capture antibody is generally perceived as crucial to the development of non-competitive immunoassays combining very high sensitivity with relatively short incubation times. (See for example Hay et al. "American Thyroid Association Assessment of Current Free Thyroid Hormone and Thyrotropin Measurements and Guidelines for Future Clinical Assays" in Clinical Chemistry, Vol 37, No. 11, (1991) at pages 2002-2008.) This approach nevertheless carries disadvantages. For example, it implies heavy consumption of antibodies which may be scarce and costly to produce. It also involves the use of various stratagems to maximise the total surface area of the solid support on which the capture antibody is deposited. For example, porous glass microspheres have been used as a solid

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Paper entitled "What's New on the Horizon", pp. 1-5, New York conference on Apr. 26-27, 1982 by William J. Dreyer.

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